Decomposition Of Field Research Articles

Numerical experiments on turbulent entrainment and mixing of scalars

Numerical experiments on the turbulent entrainment and mixing of scalars in a incompressible flow have been performed. These simulations are based on a scale decomposition of the velocity field, thus allowing the establishment from a dynamic point of view of the evolution of scalar fields under the separate action of large-scale coherent motions and small-scale fluctuations. The turbulent spectrum can be split into active and inactive flow structures. The large-scale engulfment phenomena actively prescribe the mixing velocity by amplifying inertial fluxes and by setting the area and the fluctuating geometry of the scalar interface. On the contrary, small-scale isotropic nibbling phenomena are essentially inactive in the mixing process. It is found that the inertial mechanisms initiate the process of entrainment at large scales to be finally processed by scalar diffusion at the molecular level. This last stage does not prescribe the amount of mixing but adapts itself to the conditions imposed by the coherent anisotropic motion at large scales. The present results may have strong repercussions for the theoretical approach to scalar mixing, as anticipated here by simple heuristic arguments which are shown able to reveal the rich dynamics of the process. Interesting repercussions are also envisaged for turbulence closures, in particular for large-eddy simulation approaches where only the large scales of the velocity field are resolved.

Soil macro‐ and mesofauna‐mediated litter decomposition in a subtropical karst forest

AbstractThis study aims to quantify the effect of different soil fauna on forest litter decomposition processes under natural conditions in the Maolan karst area of southwest China. Leaf litters of two typical evergreen species (CG, Cyclobalanopsis glauca and KS, Kmeria septentrionalis) were selected to conduct a field decomposition experiment using the mesh bags with three different apertures (5, 2, and 0.03 mm). Mass remaining and nutrient variation in the litterbags were determined for one year at 3‐month intervals. The results showed that litter decomposition rate in different mesh sizes litterbags were in the order of 5 mm >2 mm >0.03 mm. Soil macrofauna had a significant effect on litter decomposition in the two types of litter and the mixture of the two. The most considerable mesofauna effect was found in the KS litter, which is 36.5% ascribed by the lowest C/N ratio (high quality). Soil mesofauna had a more significant effect on N, which was time‐dependent. Moreover, the fauna richness and abundance were affected by the decomposition time but not limited by the litter quality. This study illustrated that soil macrofauna has a significant influence on litter decomposition. The effect of mesofauna on litter mass loss and nitrogen release are determined by litter quality in the subtropical karst forest ecosystems.Abstract in Chinese is available with online material.

Decomposition of Velocity Field Along a Centerline Curve Using Frenet-Frames: Application to Arterial Blood Flow Simulations

This paper presents a novel method for the evaluation of three-dimensional blood-flow simulations based, on the decomposition of the velocity field into localized coordinate systems along the vessels centerline. The method is based on the computation of accurate centerlines with the Vascular Modeling Toolkit (VMTK) library, to calculate the localized Frenet-frames along the centerline and the morphological features, namely the curvature and torsion. Using the Frenet-frame unit vectors, the velocity field can be decomposed into axial, circumferential and radial components and visualized in a diagram along the centerline. This paper includes case studies with four idealized geometries resembling the carotid siphon and two patient-specific cases to demonstrate the capability of the method and the connection between morphology and flow. The proposed evaluation method presented in this paper can be easily extended to other derived quantities of the velocity fields, such as the wall shear stress field. Furthermore, it can be used in other fields of engineering with tubular cross-sections with complex torsion and curvature distribution.

Effects of geometric and operational uncertainties on aerodynamic performance of centrifugal compressor stage

No real centrifugal compressor can exactly conform to its design geometry and expected operating conditions due to the uncertainties existing in the manufacturing and operational processes. Such uncertainties have been increasingly recognised to be detrimental to compressor performance. However, quite few studies have focused on the combined effects of geometric and operational uncertainties on compressor performance, and the underlying flow mechanism even remains unclear. In this context, we here present an uncertainty analysis of a centrifugal compressor stage, with both geometric and operational uncertainties taken into account. With the combination of CFD simulation and nonintrusive sparse grid based stochastic collocation methods, the combined and individual effects of total inlet temperature, total inlet pressure, outlet mass flow, impeller tip clearance and hub fillet radius on the stage/impeller performance are quantified and analysed. Particular attention is paid to elucidating the compressor performance variations through flow field and energy decomposition analyses. Results show that the considered uncertainties exert more influence on the compressor stage performance rather than on the impeller performance. Amongst the examined uncertainties, the impeller tip clearance contributes the most to the stage performance. The underlying mechanism lies in that the wake of impeller tip clearance produces distorted flow downstream towards the diffuser, which causes complicated vortex structures and less conversion of kinetic energy to pressure rise in the diffuser passage. The present study lays a theoretical foundation for the further uncertainty quantification and robust design of centrifugal compressors against various sources of uncertainties.

Emerging Challenges in Rural Non-Farm Sector and Inequality in Rural India

Purpose: This paper highlights the changing patterns of income diversification and the effects of various socio-economic factors influencing the non-farm (NF) income of rural households in India. The study also explores the inequality effects of the non-farm earnings of the households by using the Fields inequality decomposition. 
 Method: The study compares and evaluates the determinants and trends of inequality in 2004-2005 and 2011-2012 in the NF sector. It uses nationally representative data from two rounds of the Indian Household Development Survey (IHDS), which includes a panel of 36,278 households at all levels in India. The Censored Least Absolute Deviation (CLAD) model is used to estimate household determinants for non-farm income. The Fields decomposition decomposes total income inequality by considering the socio-economic factors.
 Results: The study finds that variations in non-farm earnings have increased. Field's Income Inequality Decomposition estimates show that income inequalities between households are significantly high due to factors such as education, level of the household head, land ownership, and population density, but also appear to be declining in 2011-12. Also, the earning gaps based on gender, age, and geographical zones have increased. 
 Implications: Overall, the non-farm income during the studied period was observed to be biased towards the better-off households. However, it opened up opportunities for underprivileged households as well. The non-farm sector has huge potential in augmenting incomes for unprivileged rural households. Therefore, the government should pay attention to this sector as a means of reducing income inequality and alleviating poverty.

Ecological stoichiometry ofCinnamomum migaoleaf litter and soil nutrients under nitrogen deposition in a karst region

AbstractNitrogen (N) deposition, a major phenomenon of climate change, is increasing with industrialization and more human activity and can affect litter decomposition. Yet it remains unclear whether N deposition will accelerate or inhibit the decomposition of litter in karst regions, which are characterized by P‐limitation or N and P co‐limited stress conditions in soil. Here, to document the influence of simulated N deposition on litter decomposition in karst, the leaf litter ofCinnamomum migaowas studied, this being a dominant perennial woody plant endemic to karst landforms. We conducted a 300‐d field decomposition experiment with four treatments: control (CK); addition of (+) N at 50 kg⋅ha−1⋅a−1(N1); +N at 150 kg⋅ha−1⋅a−1(N2), and +N at 300 kg⋅ha−1⋅a−1(N3), in southwest Guizhou, the largest karst region in China (n = 4 treatments). From each treatment, the litter samples’ remaining mass were measured during the decomposition period, in addition to their nitrogen (N), phosphorus (P), carbon (C), and potassium (K) concentrations, as well as that of soils; the soil’s pH was also measured. The results showed that litter remaining mass increased significantly under nitrogen deposition, which, as expected, acidified the soil. Meanwhile, litter N, P, and K contents responded to nitrogen deposition, whereas C did not. Otherwise, no direct effects of nitrogen deposition upon soil nutrients were detected. The soil nutrient contents were related to the release of the elements in litter. In conclusion, nitrogen deposition suppressed the decomposition ofC. migaolitter in karst, but the nutrients of karst soil are mainly replenished by litter inputs.

Thermal decomposition of the chloride and nitrate adducts of pentaerythritol tetranitrate in air at ambient pressure using a cross flow design tandem ion mobility spectrometry

The thermal decomposition of the chloride adduct of pentaerythritol tetranitrate (PETN) has been studied with a new cross-flow sample introduction, dual shutter, ion mobility spectrometer. Chloride anions, produced in an ion source, react with PETN introduced by a nebulizer into a flow of heated gas orthogonal to the drift gas flow. This cross-flow procedure allows PETN introduction from solution at drift gas temperatures where the PETN∙Cl¯ intensity is sufficiently intense and stable to allow characterization of its thermal decomposition kinetics. Dual shutter operation allows the selection of PETN∙Cl¯ for observation of its thermal decomposition in the electrostatic drift field. In this adduct, Cl¯ displaces NO3¯ in an SN2 reaction with an activation energy of 80 ± 7 kJ mol-1 over the temperature range 145 °C–165 °C. At temperatures above 165 °C, decomposition occurs before ion selection, resulting in the release of NO3¯ and PETN∙NO3¯ becomes the sole adduct ion. PETN∙NO3¯ decomposes over the temperature range 175 °C–200 °C with an activation energy of 92 ± 8 kJ mol-1. Density functional calculations are used to interpret the results.

Effect of uniform incoming flow on vehicle’s hydrodynamics under the same relative velocity

At present, the effect of a uniform stream on the hydrodynamic force or moment under the same relative velocity has been studied mostly in inviscid flow and the results are not consistent. To build the relative motion principle in viscous flow, the relationship of flow fields between the non-stream circumstance and stream circumstance is constructed and the flow field of the steam circumstance is decomposed into the corresponding rest far-field flow and the stream field. Then, hydrodynamic force and moment formulas that are linearly dependent on the distribution of flow field and valid in both viscous and inviscid flow are proposed. Subsequently, the hydrodynamics in the stream circumstances is decomposed according to the flow field decomposition and the uniform stream’s effect is clarified. The correctness of the acquired hydrodynamics transformation formulas is verified by comparing numerical results in both inviscid and viscous flow. At last, the validity of the existing relative motion principle is confirmed or analyzed.

Impacts of Salinity Variation on the Mixed‐Layer Processes and Sea Surface Temperature in the Kuroshio‐Oyashio Confluence Region

AbstractIn this study, salinity variations in the Kuroshio–Oyashio confluence region (KOCR) are examined through analyses of observational datasets and an ocean reanalysis product, and their potential impacts on sea surface temperature are assessed by sensitivity experiments using a one‐dimensional mixed layer model (1‐D ML model). We have detected prominent covariations in near surface temperature and salinity in the KOCR during the boreal winter to spring. Further investigation revealed that such covariations are closely related to the dynamical stability of the Kuroshio Extension (KE), and anomalous warming and salinification (cooling and freshening) are observed in the KOCR when the upstream of the KE is in an unstable (a stable) state. It is found that modulation heat and freshwater transport by mesoscale eddies and large‐scale current anomalies are closely related to such observed variation. Then, we have quantitatively estimated the impacts of these salinity variations on local density by a detailed decomposition of total anomaly fields. Although the total density anomalies are dominated by contributions from temperature, the salinity contribution has sizable magnitude especially in the northern part of the KOCR, where the background temperature is low and the dependence of density on temperature variations is weak. To further quantify the impact of salinity anomalies, we conducted a series of sensitivity experiments utilizing the 1‐D ML model. The results from these experiments revealed that salinity anomalies significantly alter the strength of vertical mixing and eventually lead to differences in sea surface temperature of approximately 1.0°C.

Spherical harmonic decomposition of a sound field based on observations along the equator of a rigid spherical scatterer.

We present a method for computing a spherical harmonic representation of a sound field based on observations of the sound pressure along the equator of a rigid spherical scatterer. Our proposed solution assumes that the captured sound field is height invariant so that it can be represented by a two-dimensional (2D) plane wave decomposition (PWD). The 2D PWD is embedded in a three-dimensional representation of the sound field, which allows for perfectly undoing the effect of the spherical scattering object. If the assumption of height invariance is fulfilled, then the proposed solution is at least as accurate as a conventional spherical microphone array of the same spherical harmonic order, which requires a multiple of the number of sensors. Our targeted application is binaural rendering of the captured sound field. We demonstrate by analyzing the binaural output signals that violations of the assumptions that the solution is based on-particularly height invariance and consequently also horizontal propagation-lead to errors of moderate magnitude.

Analysis of the Contribution of Large Scale Motions to the Skin Friction of a Zero-Pressure-Gradient Turbulent Boundary Layer Using the Renard-Deck Decomposition

Coherent flow structures in turbulent boundary layers have been an active field of research for many decades, as they might be the key to reveal the mechanics of turbulence production and transport in turbulent shear flows. Renard and Deck (2016) proposed a theoretical decomposition for the mean skin-friction coefficient based on the mean kinetic energy budget in the streamwise direction. This decomposition, referred to as the Renard-Deck (RD) decomposition, decomposes the mean skin friction generation into three physical mechanisms in an absolute reference frame, namely, direct viscous dissipation, turbulent kinetic energy production, and spatial growth. In this study, the large scale motions (LSMs) are extracted using a proper orthogonal decomposition (POD) of the velocity field based on high-spatial-resolution two-dimensional – two-component particle image velocimetry (HSR 2C-2D PIV) of a zero-pressure-gradient turbulent boundary layer (ZPG-TBL), and their effect on the skin friction via RD decomposition.

Bayesian calibration of order and diffusivity parameters in a fractional diffusion equation

This work focuses on parameter calibration of a variable-diffusivity fractional diffusion model. A random, spatially-varying diffusivity field with log-normal distribution is considered. The variance and correlation length of the diffusivity field are considered uncertain parameters, and the order of the fractional sub-diffusion operator is also taken uncertain and uniformly distributed in the range . A Karhunen-Loève (KL) decomposition of the random diffusivity field is used, leading to a stochastic problem defined in terms of a finite number of canonical random variables. Polynomial chaos (PC) techniques are used to express the dependence of the stochastic solution on these random variables. A non-intrusive methodology is used, and a deterministic finite-difference solver of the fractional diffusion model is utilized for this purpose. The PC surrogates are first used to assess the sensitivity of quantities of interest (QoIs) to uncertain inputs and to examine their statistics. In particular, the analysis indicates that the fractional order has a dominant effect on the variance of the QoIs considered, followed by the leading KL modes. The PC surrogates are further exploited to calibrate the uncertain parameters using a Bayesian methodology. Different setups are considered, including distributed and localized forcing functions and data consisting of either noisy observations of the solution or its first moments. In the broad range of parameters addressed, the analysis shows that the uncertain parameters having a significant impact on the variance of the solution can be reliably inferred, even from limited observations.

The influence of aspect ratio on flow states in the buoyancy-driven turbulence with free slip boundaries

Buoyancy driven turbulence with free-slip top and bottom plates in a confined box is studied via direct numerical simulations (DNS). The Rayleigh number is fixed to Ra=108 and the Prandtl number is Pr=10. The length/height aspect ratio Γy is fixed to 2, while the depth/height aspect ratio Γx varies from 0.125 to 0.3. With the variation of Γx, the hysteresis-like behavior of the heat and momentum transfer is found due to the emergence of two stable states of flow organization. For small Γx, the sheared flow occurs with disordered plumes occupying the entire bulk region, while it is replaced by convection rolls with increasing Γx. The striking feature is that the heat and momentum transport is greatly suppressed in the shear flow (SF) state, compared with that in the convection roll (CR) state. The turbulent kinetic energy budget is performed to delineate the relative contributions of physical processes that govern energy transport. It is found that the kinetic energy in the SF state is mainly produced by the buoyancy force, while it is dominated by the shear production near the plates in the CR state. During energy transport, it seems that the buoyancy force plays a more important role in the SF state than in the CR state, particularly in the bulk. Furthermore, through the analysis of dynamic mode decomposition of temperature fields, we illustrate that the flow in the SF state is dominated by the cloud-like spatially coherent structures with low frequencies, while the low-frequency roll structures play a leading role in the CR state. The flow state transition from SF to CR corresponds to the process that the cloud-like coherent structures form roll structures.

Modal decomposition of the pressure field on a bridge deck under vortex shedding using POD, DMD and ERA with correlation functions as Markov parameters

A pressure field on a stationary bridge section with a clear signature from vortex shedding is obtained from a numerical simulation. The pressure field is subjected to modal decomposition using the snapshot prober orthogonal decomposition method (POD), the exact dynamic mode decomposition method (DMD) and a novel application of the eigenvalue realization algorithm (ERA) where the correlation functions of the pressure field is used as Markov parameters. All three methods are able to identify spatial mode shapes of the surface pressure field due to vortex shedding. The Strouhal number is estimated using dynamic mode decomposition and the eigenvalue realization algorithm where the latter is the most accurate and precise method. Finally, the ERA is applied to estimate Strouhal numbers and vortex shedding pressure mode shapes under different flow conditions in wind tunnel and full-scale testing of the Gjemnessund bridge in Norway.

Field Decomposition of Corn Cob in Seasonally Frozen Soil and Its Intrinsic Influencing Factors: The Case of Northeast China

Returning corn cobs to the field during corn kernel harvesting is an effective way to improve soil properties and increase crop yield. However, seasonally frozen soil seriously hinders the field decomposition process of corn cobs. To explore the decomposition characteristics and promote field decomposition, in this study, the nylon mesh bag method was used to perform field decomposition tests for 150 days. Fiber composition analysis and microstructure observation were carried out. The results showed that the field decomposition of corn cob was influenced by temperature, precipitation, and frozen soil environment. The 150-day cumulative decomposition rates of the pith, woody ring, and glume were 40.0%, 24.2%, and 36.3%, respectively. Caused by the difference in fiber compositions, the decomposition speeds of pith and glume were much higher than that of the woody ring. The complex microstructures of the pith, woody ring, and glume led to differences in the accessibility of cellulose, which indirectly influenced the field decomposition characteristics. The homogeneous sponge-like structure of the pith and glume increased the accessibility of cellulose and ultimately accelerated the field decomposition, while the compact lignocellulosic structure of the woody ring hindered the decomposition process. Compared with corn stalk, corn cob had similar or even better field decomposition characteristics and excellent application prospects.

Experimental investigation on the effect of particles on large scale vortices of an isolated hemispherical roughness element

Particle image velocimetry (PIV) was used to investigate the effect of 155 μm polystyrene particles on the wake structure of an isolated hemispherical roughness element placed in a laminar boundary layer of a flat plate. The main purpose of this study was to investigate the influence of particles on the large-scale vortices induced by the hemisphere. The turbulence statistics and the main modes of proper orthogonal decomposition (POD) in whole field of view (FOV) were comparatively analyzed. The shedding frequency was analyzed by the power spectral density (PSD) function, and the hairpin vortex head structure was conditionally detected by the spatial multi-scale local average function. The results showed that by introducing particles, the statistics in the near-wall region downstream of the hemisphere were significantly changed. PSD results showed that the existence of particles led to the shedding of structures with multiple frequencies and inhibited the shedding of primary structures. Further conclusions could be drawn through POD and hairpin vortex head extraction: the existence of particles changed the type of vortex shedding behind the hemisphere, thereby reducing the number and the vorticity intensity of hairpin vortex heads in the range near the peak, and promoting the scale of the prograde vortex structure.

Wavelet field decomposition and UV \u2018opaqueness\u2019

A large body of work over several decades indicates that, in the presence of gravitational interactions, there is loss of localization resolution within a fundamental (∼ Planck) length scale ℓ. We develop a general formalism based on wavelet decomposition of fields that takes this UV ‘opaqueness’ into account in a natural and mathematically well-defined manner. This is done by requiring fields in a local Lagrangian to be expandable in only the scaling parts of a (complete or, in a more general version, partial) wavelet Multi-Resolution Analysis. This delocalizes the interactions, now mediated through the opaque regions, inside which they are rapidly decaying. The opaque regions themselves are capable of discrete excitations of ∼ 1/ℓ spacing. The resulting effective Feynman rules, which give UV regulated and (perturbatively) unitary physical amplitudes, resemble those of string field theory.

Understanding Optical Absorption Spectra and Magnetic Behavior of a Wide Range of Samarium(III) Oxo‐Compounds: Analysis of the Ligand‐Field Effects

AbstractIn this study powder reflectance spectra as well as temperature dependent magnetic susceptibilities of eight different samarium(III) oxo‐compounds (SmP5O14, SmPO4, SmVO4, SmNbO4, SmTaO4, Sm2Ti2O7, SmAsO4, B‐type Sm2O3 and C‐type Sm2O3) have been measured. In addition, high‐resolution electronic absorption spectra in the near infrared of single crystals of seven of these compounds are reported. Comparing our experimental data to the results of ligand field analyses (angular overlap model AOM allowing for decomposition of the global ligand field into the contributions of the individual ligands; computer program BonnMag) shows reasonable agreement of electronic transition energies in optical spectra and a good fit of the temperature dependent Bohr magneton numbers μeff/μB. Analysis of the ‘best fit’ AOM parameters reveals a significant variation in the nephelauxetic effect with F2=379 cm−1 for SmP5O14 and F2=356 cm−1 for KSmO2. A trend in the variation of the AOM parameter eσ with the optical basicity Λ is discussed. The values for eσ(Sm−O), normalized to d(Sm−O)=2.38 Å, range from 337 cm−1 for SmP5O14 to 573 cm−1 for KSmO2. For the ratio eπ/eσ only a negligible influence on the match between calculated and experimental data is observed. For the relation of eσ(Sm−O) to the interatomic distance d(Sm−O) the correlation eσ(Sm−O) ∼1/d7(Sm−O) was found to reproduce in AOM the observed ligand field splitting well. For SmPO4 a high resolution, low temperature (110 K) spectrum allows the assignment of hot bands.

Equivalence between angular spectrum-based and multipole expansion-based formulas of the acoustic radiation force and torque.

Two main methods have been proposed to derive the acoustical radiation force and torque applied by an arbitrary acoustic field on a particle: The first one relies on the plane wave angular spectrum decomposition of the incident field (see Sapozhnikov and Bailey [J. Acoust. Soc. Am. 133, 661-676 (2013)] for the force and Gong and Baudoin [J. Acoust. Soc. Am. 148, 3131-3140 (2020)] for the torque), while the second one relies on the decomposition of the incident field into a sum of spherical waves, the so-called multipole expansion (see Silva [J. Acoust. Soc. Am. 130, 3541-3544 (2011)] and Baresch, Thomas, and Marchiano [J. Acoust. Soc. Am. 133, 25-36 (2013)] for the force, and Silva, Lobo, and Mitri [Europhys. Lett. 97, 54003 (2012)] and Gong, Marston, and Li [Phys. Rev. Appl. 11, 064022 (2019)] for the torque). In this paper, we formally establish the equivalence between the expressions obtained with these two methods for both the force and torque.

Honey, I Shrunk the Domain: Frequency‐aware Force Field Reduction for Efficient Fluids Optimization

AbstractFluid control often uses optimization of control forces that are added to a simulation at each time step, such that the final animation matches a single or multiple target density keyframes provided by an artist. The optimization problem is strongly under‐constrained with a high‐dimensional parameter space, and finding optimal solutions is challenging, especially for higher resolution simulations. In this paper, we propose two novel ideas that jointly tackle the lack of constraints and high dimensionality of the parameter space. We first consider the fact that optimized forces are allowed to have divergent modes during the optimization process. These divergent modes are not entirely projected out by the pressure solver step, manifesting as unphysical smoke sources that are explored by the optimizer to match a desired target. Thus, we reduce the space of the possible forces to the family of strictly divergence‐free velocity fields, by optimizing directly for a vector potential. We synergistically combine this with a smoothness regularization based on a spectral decomposition of control force fields. Our method enforces lower frequencies of the force fields to be optimized first by filtering force frequencies in the Fourier domain. The mask‐growing strategy is inspired by Kolmogorov's theory about scales of turbulence. We demonstrate improved results for 2D and 3D fluid control especially in higher‐resolution settings, while eliminating the need for manual parameter tuning. We showcase various applications of our method, where the user effectively creates or edits smoke simulations.